I'm re-landscaping my front yard and will have someone do the irrigation for me. To save costs I agreed to dig the trench for the main line. I chose to do it along the fence line as there was a massive root left from a photinia i got stumped that i couldnt remove on the other side. (I've gone 150-200mm deep for the trench - twice as deep for the valve box).
However, now that I've started to plant my Viburnum Tinus hedging I'm concerned that they will be too close to the mainline + wiring once they are in the trench. Here's a snap for a visual - http://imgur.com/a/FgTmU. I mentioned it to the irrigation installer and he said they could run it above ground as close to the fence line as possible but under mulch etc to avoid exposure) and then bring it underground to the valve box & garden tap.
I'm new to the caper but googling around I couldn't find any examples of main line irrigation being above ground - and common sense would suggest you want it underground to avoid weather exposure or accidental damage.
So 2 questions -
1. Is above ground an option for irrigation main line + wiring?
2. How do people go about avoiding root damage when needing to run the main line or any subsurface irrigation near trees or where trees/plants will be growing? It's possible i just need to dig the trench deeper.